As is known in the art, many electronic devices require a bias voltage source to enable such device to operate in a desired operating region. For example, a transistor used to linearly amplify an input signal generally requires a bias voltage to enable the transistor to operate in its linear operating region.
More particularly, in one example, Depletion mode (D-Mode) MESFETS and HEMTS in some applications are required to operate with drain voltages set to a positive potential, sources set to ground and a negative bias (lower potential than Ground) applied to the gate. When D-mode FETS are used discretely or in integrated circuits any negative DC bias typically comes from an external negative power supply in addition to the positive DC supplies and ground connection.
There are two common approaches for supplying a negative DC bias to Depletion Mode FETS. The most common approach is an “off-chip” external DC power supply. A second more compact and integrated approach may use a DC-DC converter circuit requiring transistors, resistors, large capacitors, an oscillating signal and positive DC supply.
As is also known in the art, one source of electric potential is thermoelectric. One thermoelectric effect is the Seebeck effect. More particularly, a linear certain material combinations, called thermojunctions. A thermocouple is a device for measuring temperature that is made up of one or more thermoelectric junctions. Thermojunctions respond to this thermal gradient with a detectable voltage. It is based on the Seebeck effect (measured in volts per degree C.) in which a voltage appears between two dissimilar materials if a temperature gradient exists between two junctions along them. Sometimes many pairs of junctions or thermocouples are connected in series, where the net thermoelectric voltage produced by one thermocouple adds to that to the next, and so on. This multiple series connection yields a larger thermoelectric output. Such a series of thermocouple connections is called a thermopile. Thermopiles are place in close proximity to a heat source, usually a thin film resistor. The thermoelectric sensitivity would be equal to the voltage detected divided by power dissipated in heat source in V/W. Parameters employed to maximize thermopile thermoelectric output are: the number of thermopiles, thermopile length, thermopile width, thermopile pitch, and proximity to heat source.
As shown in the equations below, the sum of the temperature differentials (Ti, To) between the hot and cold junctions for a series of thermocouples is multiplied by the Seebeck coefficient (αk) to yield a detected voltage (Vout) for the thermopile. The sensitivity (S) is equal to the detected voltage divided over the power dissipated.
      Seebeck    ,                  ⁢                  α        tc            ∼              300        ⁢                                  ⁢        μV        ⁢                  /                ⁢        C                        V      out        =                  α        tc            ⁢                        ∑                      i            =            1                    N                ⁢                  (                                    T              i                        -                          T              o                                )                          Sensitivity    ,                  ⁢          S      =                        V          out                /                  P          diss                      ,                  ⁢          (              V        /        W            )      
As is known in the art, such thermopiles have been suggested for use as thermal sensors, reference being made to the following articles: “Broadband thermoelectric microwave power sensors using GaAs foundry process” by Dehe, A.; Fricke-Neuderth, K.; Krozer, V.; Microwave Symposium Digest, 2002 IEEE “MTT-S International, Volume: 3, 2002 Page(s): 1829-1832; “Free-standing Al0.30Ga0.70As thermopile infrared sensor”, by Dehe, A.; Hartnagel, H. L.; Device Research Conference, 1995. Digest. 1995 53rd Annual, 19-21 Jun. 1995 Page(s): 120-12; and “High-sensitivity microwave power sensor for GaAs-MMIC implementation” by Dehe, A.; Krozer, V.; Chen, B.; Hartnagel, H. L.; Electronics Letters, Volume: 32 Issue: 23, 7 Nov. 1996 Page(s): 2149-215, and an article by A. Dehe et al., entitled “GaAs Monolithic Integrated Microwave Power Sensor in Coplanar Waveguide Technology” published in the IEEE 1996 Microwave and Milli-meter Wave Monolithic Circuits Symposium, pages 179-181.